Competition For Access To Roots Can Affect Inoculant Performance

Finding a way to make nitrogen-fixing bacteria more competitive once they are added to the soil has been one of the hardest problems for seed inoculant companies to overcome. Special strains of the newly added bacteria, called rhizobia, are specificallyselected for their strong ability to remove nitrogen from the air and “fix” it into a form can be used by plants. These strains perform very well in controlled laboratory settings. The problem begins once the bacteria has been applied to the field.

Soils contain an infinite number of bacteria and other microscopic life, which creates a very harsh and competitive life in the soil. Many species of these naturally-occurring bacteria live by colonizing the roots of plants and forming symbiotic relationships with the plant. When a seed inoculant is applied, the newly added rhizobia also need to colonize the plant roots in order to form nodules. This creates an intense competition between all bacteria for access to the roots. The new rhizobia, while skilled at nitrogen fixation, are not naturally competitive, especially against a soil’s native bacteria. This can potentially hinder the effectiveness of the inoculant.

Generally, the strategy of inoculants has been to find ways to help the new rhizobia outcompete the native bacteria. This could be by applying overwhelming numbers of bacteria to the seed in order to increase the chances of nodulation, or by working to suppress the activity of the native bacteria. More recently, formulations such as AGPT (Advanced Growth Promoting Technology) from XiteBio Technologies have been designed to avoid competition and instead work together with what’s already in the soil and create a syngergistic relationship. With the bacteria no longer spending energy to fight each other, they are more easily able to colonize the plant roots and share their growth promoting benefits with the crop.